Top End speed loss with fins

[Belleville_Boater]

Took my 212X in for it's 10-hour maintenance and I also installed cobra fins when I got it home. LOVE the fins, they made a huge difference and the wife isn't afraid to drive anymore. I currently have the fins set to be down all the time, what kind of speed loss are you guys seeing? I had it WOT last night and only got up to 45-47 MPH rather then the typical 55. Not complaining about the fins, they were well worth it, but just wanted to know if the 10MPH loss is what others are seeing? Thinking maybe I should adjust it to not be down all the time but pop up at speed, your thoughts?

 

[itsdgm]

You and I have very different boats and I have the older style fixed cobra fins and I get the same top speed 45MPH with or without fins. So I can't imagine that your 10 mph drop would be caused by the fins.

 

[Glassman]

I too have the fixed fins, original ones at that. They are completely out of the water at WOT. They make zero difference in my top speed...which, according to my GPS kissed 50 Saturday morning in the cool air and flat water.
That made me happy.
It made my son in law sad.

 

[OrangeTJ]

What u r experiencing may actually be due to your nozzles not being perfectly aligned. Somehow the nozzles on my 210 have gotten a bit out of whack, such that they both point slightly toward eachother when the wheel is centered. This means that the fins are dragging slightly askew through the water. I had lost about 10mph in top speed from my 210 compared to last year. After pulling it out of the slip for the first time in a couple of months I found a fair amount of algae buildup and that my nozzles are out of alignment. My hull cleaner hasn't come in yet so I have not been able to get all of the scum off but I did flip my cobras up prior to this past weekends boating trip. This outing, despite going from 400 feet elevation to 4000 feet elevation, I got 5 mph more speed on top!

 

[Belleville_Boater]

What u r experiencing may actually be due to your nozzles not being perfectly aligned.

I was thinking that also, just eyeballing it from the back after putting the fins on seemed like they weren't exactly parallel to each other which I figured would cause some drag and speed loss. I can't say i loved the steering at high speed with the fins down anyway so having them kick up may be a nice all around adjustment.

 

[Julian]

Somehow the nozzles on my 210 have gotten a bit out of whack, such that they both point slightly toward eachother when the wheel is centered.

There was discussion about this on some other site way back. An Australian jet boat racer mentioned that the nozzles actually SHOULD be pointing together slightly.....I forget the specific degrees referenced, but it was an interesting discussion.

 

[Belleville_Boater]

That would be an interesting read, if you happen to find that article please post.

 

[Julian]

Here is what is in the service manual for my boat:

 

[Julian]

I'm blocked from logging in over there, and although I can bypass his stupid IP block on my office machine, I refuse to....

But a google search tells me it is this thread:

http://yamahajetboaters.com/forum/viewtopic.php?f=7&t=21231

If it is, please write up the pertinent details over here so we all can refresh our memories (as who knows how much longer that site will exist)

 

[Cobra Jet Steering LLC]

We have never had a g p s test show any loss of speed with the fins all the way down , Perhaps you can try lifting them up and do a test run I seriously doubt the fins are causing any top end speed reduction.

 

[Belleville_Boater]

We have never had a g p s test show any loss of speed with the fins all the way down , Perhaps you can try lifting them up and do a test run I seriously doubt the fins are causing any top end speed reduction.

Definitely planning on doing that (hopefully next weekend), going to just rotate the actuator to the new holes and see how that runs. LOVE the fins though, it has made a noticeable difference and was a great investment. If the wife is actually HAPPY about them then that is a huge accomplishment lol.

 

[Cobra Jet Steering LLC]

Yes you have the new 7 hole set so let me know how you like the new setting it will keep just a small amount of the fins in contact with the water at speed and they kick up later than the 6 hole set.
However I doubt you will see a difference in top end either way , on plane the only fin making contact with the water is the outer fin , the fins are only 3/16 of an inch thick with no obstructions making any contact with the water to cause any excess drag or water disruptions, the leading edges are continuous with no cut outs to cause drag either . As for aligning the nozzles You simply place the wheel in a dead center position and tie it in place using a good bungee cord , place the controls in forward to get the reverse hoods up out of the way, be sure to check that both hoods are even and up out of the way of the water exiting the nozzle when the controls are both in forward.
Place a straight edge " a long level works good" across the openings of the 2 nozzles and if they are aligned properly the straight edge will make contact with all 4 sides of the nozzles evenly, if they are out of alignment you will see it miss one or two edges.

 

[Julian]

I'm blocked from logging in over there, and although I can bypass his stupid IP block on my office machine, I refuse to....

But a google search tells me it is this thread:

http://yamahajetboaters.com/forum/viewtopic.php?f=7&t=21231

If it is, please write up the pertinent details over here so we all can refresh our memories (as who knows how much longer that site will exist)

Now I'm home and have easier access here, that is not the thread with the Australian jet boat racer who posted about how nozzles on twin engines should be angled inwards....sorry. Can't find that thread either.

 

[Belleville_Boater]

Thanks for looking at least!

 

[CrankyGypsy]

Here is what is in the service manual for my boat:

View attachment 24044

Maybe you bumped the gates and they are sitting more in the jet stream?
just want to mention in case you start playing with the gates: i just replaced the reverse cables and i found that if i went by the manual, it greatly hindered my ability to raise the gate beyond the nozzle stream. i got mine to come nearly level with the top of the nozzle. granted, this may have thrown my true neutral off (though i've not noticed yet). testing on the trailer, if i nudge the throttles back a bit before the reverse detent, it will drop to factory height. ANYWAYS, in order to get more wiggle room at the gate, i had to engage 16mm of thread beyond the "locking" nut at the throttle (just like in the pic above, except 16mm instead of 8mm). this still allowed me to get at least 8mm of engagement at the nozzle for factory height AND add a little more to clear the nozzles.

 

[Englewoodcowboy]

Following this one.

 

[Cobra Jet Steering LLC]

I have been watching this for any updates, I did read that you had it serviced and added the fins at the same time, I would be looking at things like overfilled oil , that will cut your top end speed instantly . There are thousands of people with that system on their boats with no issues of the top end being effected.

 

[Noko]

I'm blocked from logging in over there, and although I can bypass his stupid IP block on my office machine, I refuse to....

But a google search tells me it is this thread:

http://yamahajetboaters.com/forum/viewtopic.php?f=7&t=21231

If it is, please write up the pertinent details over here so we all can refresh our memories (as who knows how much longer that site will exist)

You are BLOCKED?!!! OMG! There is another jet boat site? I never knew.Well, I did, that's why I'm here.

I have Thrust Vectors that retract as you go faster. I would doubt though that fins being in the full down position would take 10kts off your top speed. I notice the more people I have and water conditions affect my boat more. I usually get 44-48kts with my California boat. I've hit 50kts when its been just me and the lake was calm. My engines put out about 7,400 rpm and my lake is at 900' MSL. 48kts is just fine and I don't run at that speed much, the boat cruises really nice at 30kts.

 

[Julian]

You are BLOCKED?!!! OMG! There is another jet boat site? I never knew.Well, I did, that's why I'm here.

I have Thrust Vectors that retract as you go faster. I would doubt though that fins being in the full down position would take 10kts off your top speed. I notice the more people I have and water conditions affect my boat more. I usually get 44-48kts with my California boat. I've hit 50kts when its been just me and the lake was calm. My engines put out about 7,400 rpm and my lake is at 900' MSL. 48kts is just fine and I don't run there much, the boat cruises really nice at 30kts.

Yup, I was banned and IP blocked for sticking up for other banned members....

He censors posts with our URL and we added links to his site and store....open and democratic will always win!

Yeah....agree that fins can't be responsible for that kind of speed loss.

 

[JimG]

@Belleville_Boater : Did you ever get a chance to lift up the fins and see what speed you get? I have never driven my boat without the Cobra Ultimates, and the max speed I get is 47ish. Like yours, I have mine set in the all-the-way down position.